1. Field of the Invention
The present invention relates to a bipolar transistor and particularly, to a bipolar transistor in which impurities are introduced from emitter electrode material in which the impurities are introduced, thereby forming an emitter region.
2. Description of the Related Art
FIG. 1 shows the structure of a conventional bipolar transistor.
As shown in FIG. 1, collector region 2 is provided on N+substrate 1, and element separating oxide film 3 is provided on the collector region 2. Electrode 11 is provided above emitter region 10 and base region 5 through oxide film 4 and nitride film 6.
The oxide film 4 and the nitride film 6 are perforated to form base contact hole 7 for connecting the base region 5 and the electrode 11 and emitter contact hole 8 for connecting the emitter region 10 and the electrode 11. The emitter contact hole 8 is buried with polysilicon (polycrystal silicon) containing arsenic with which the emitter region 10 is formed, and the electrode 11 is provided on the polysilicon 9. The base contact hole 7 is buried with the conductive material of the electrode 11.
Japanese Laid-open Patent Publication No. Hei-6-291133, Japanese Laid-open Patent Publication No. Hei-7-130760, Japanese Laid-open Patent Publication No. Hei-8-335584, Japanese Examined Patent Publication No. Hei-7-123126 disclose techniques pertaining to the present invention.
In the technique shown in FIG. 1, if the overall device is designed in a microstructure in order to form the base contact hole 7 and the emitter contact hole 8 on the base region 5 and the emitter region 10 at the same time in a dry etching process, the emitter contact hole 8 would be narrow. In addition, the area of the emitter region would be small because the emitter region is formed by introducing impurities of polysilicon 9 in the emitter contact hole 8.
An object of the present invention is to provide a bipolar transistor in which the area of an effective emitter region can be increased without narrowing an emitter contact hole.
In order to attain the above object, according to the present invention, there can be provided a bipolar transistor includes an emitter region formed in a base region; a first insulating film formed on the emitter region so as to have a first opening portion provided on the emitter region; and a second insulating film formed on the first insulating film so as to have a second opening portion smaller than the first opening portion provided on the first opening portion, wherein emitter electrode material doped with impurities is buried in the first and second opening portions.